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Thursday, May 30, 2013

Arapaima: One of the largest freshwater fish in the world

Lurking in the lakes and rivers of the Amazon basin are
some of the most unusual fish you are likely hear about. Arapaima have been
recorded up to 3 meters in length and over 200 kg. This fish has been featured
on River Monsters and its history is deeply rooted in local tribal traditions.
In addition, its biology could be considered unusual.

Due to the long history of being an important indigenous
food source, arapaima are one of the few fish which are threatened in their
home range while simultaneously being of management concern outside of its
native region. Bolivia and Peru both show some evidence that this non-native
piscivore can deplete populations of native game fish. This polarity of concern
makes policy and management, especially outside the Amazon basin, a difficult
task. While much is known about arapaima biology, population estimates can be
tricky due to its widespread nature. It is known however, that near large human
developments, this fish is functionally extinct. Restrictions on size and
season are in place, but poorly enforced.

Arapaima reproduce according to the flood pulses of the mighty
Amazon basin, migrating laterally along tributaries into numerous surrounding
lakes. In February through April, when water levels are their lowest, these
fish spawn in floodplain lakes. Parental care is a large component of arapaima
biology and the young are often seen clustered around the father’s head.
Rearing of young is timed just before the rainy season comes. Males will guard
the nest and the young, and even help the offspring complete their first
migration into the tributaries as water levels rise. There is even some
observational evidence that arapaima “learn” to feed from watching their father
as they travel out of the lakes and into the rivers.

The greatest concern for the future of this fish in its
native range is due to its vulnerability to detection while guarding nests. Arapaima,
which is in the bony tongue order, is an obligate air breather, and must
surface every 10-15 minutes to breathe. The signature sucking sound is like a
dinner bell to harpooners, who have honed their skills to hunting this fish.
Historically, the best time to hunt was during the dry season when arapaima are
cut off in floodplain lakes. This is also their spawning season. Without care,
the eggs and young arapaima cannot survive, and this is the major cause of
population decline. While regulations seek to restrict hunting arapaima during
this time, there is little enforcement. When coupled with a lack of population
estimates, it is exceedingly difficult to know the current status of this fish
in its native range. It is clear however, more study is needed to determine how
threatened this species is and what level of protection is required.